From mboxrd@z Thu Jan 1 00:00:00 1970 From: rafael@kernel.org (Rafael J. Wysocki) Date: Sat, 10 Jun 2017 00:53:54 +0200 Subject: Drivers taking different actions depending on sleep state In-Reply-To: <9dc7b7f4-e47d-59f3-3b51-52e0aefd2487@free.fr> References: <9dc7b7f4-e47d-59f3-3b51-52e0aefd2487@free.fr> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi, On Fri, Jun 9, 2017 at 5:20 PM, Mason wrote: > Hello, > > I read the "Sleep States" documentation: > https://www.kernel.org/doc/Documentation/power/states.txt > > It mentions /sys/power/mem_sleep but I don't have that in 4.9 > # ll /sys/power/ > -rw-r--r-- 1 root root 4096 Jan 1 00:31 pm_async > -rw-r--r-- 1 root root 4096 Jan 1 00:31 pm_freeze_timeout > -rw-r--r-- 1 root root 4096 Jan 1 00:31 state > -rw-r--r-- 1 root root 4096 Jan 1 00:31 wakeup_count > > # cat /sys/power/state > freeze mem > > Currently my platform's "mem" is a true suspend-to-RAM trigger, > where drivers are supposed to save their state (register values > will be lost), then Linux hands control over to firmware which > enables RAM self-refresh and powers the chip down. When the system > resumes, drivers restore their state from their copy in memory. > > One driver is responsible for loading/unloading microcode running > on the DSPs. This operation is required only when powering down > the chip, but it should be avoided for "low-latency" sleeps. > > The problem is that, if I understand correctly, drivers have no way > of knowing which sleep state is being entered/exited? > > How can I have the microcode driver take different decisions > based on the sleep state? The cleanest way would be to run that code from one of the platform suspend hooks that receive information on what sleep state is to be entered. Alternatively, those hooks can set/clear flags that can be accessed by drivers, but that of course may your drivers depend on the platform (still, in the microcode case the driver seems to be platform-dependent anyway). Thanks, Rafael